Automatic common-battery telephone system.



T. G. MARTIN.

AUTOMATIC COMMON BATTERY TELEPHONE SYSTEM.

APPLICATION FILED MAY 2. I905.

1,185,521. Patented May 30, 1916.

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T. G. MARTIN. AUTOMATIC COMMON BATTERY TELEPHONE SYSTEM.

. APPLICATION FILED MAY Z. "05- Patented 30' 4 SHEETS-SHEET 2- lbw/170;; W

T. G. MARTIN.

AUTOMATIC COMMON BATTERY TELEPHONE SYSTEM. umcmon nun IAY a. 100:.

1,185,521. Patented May 30,1916.

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AUTOMATIC COMMON BATTERY TELEPHONE SYSTEM. Armcmou mm IAY 2. nos.

Patented May 30, 1916.

6 HEUS-SNEET 4.

UNITED STATES PATENT OFFICE.

TALBOT G. MABTIN, OF CHICAGO, ILLINOIS, ASSIGNOR, BY MESNE ASSIGNMENTS, TO FIRST TRUST AND SAVINGS BANK, TRUSTEE, OF CHIC AGO, ILLINOIS.

AUTOMATIC COMMON-BATTERY TELEPHONE SYSTEM.

Application filed May 2, 1905.

To all whom it may concern:

Be it known that I, TALBOT G. MARTIN, a citizen of the United States of America, and resident of Chicago, Cook county, Illinois, have invented a certain new and useful Improvement in Automatic Common-Bat tery Telephone Systems, of which the following is a specification.

My invention relates to automatic telephone systems of that particular character in which automatic switching machines are employed in place of the ordinary switchboard operators-that is to say, in which the connections at the central station or exchange are made automatically, through the medium of step-by-step switching machines, instead of through the medium of the switchboard operators ordinarily employed at manual board exchanges.

My invention relates more particularly to that type of automatic telephone systems in which the automatic switching machines are of two kinds, namely, selectors and connectors, the selectors being adapted to respond to electrical impulses projected over the line-circuits by a calling subscriber, and each selector being adapted to perform an operation in accordance with an impulse 0r impulses representing one of the digits of the called number. As distinguished from this, a connector is adapted to respond to the impulses representing the last two digits of the called number, and to make the final connection directly with the line of the called subscriber. Ordinarily, and as hereinafter explained, a selector responds to the impulse or impulses re resenting one of the first digits of the ca led number, the vertical movement of its switchshatt being under the direct control of the subscriber, so that the subscriber may pick out the desired group of trunk-lines running to other selectors, or to connectors, according to the size of the exchange. In a selector, however, the rotary movement, after the switch-shaft has been actuated to the desired level, is automatic in this respect: that the swinging or movable switch-contacts continue to move around and traverse the stationary contacts until connection is established with an idle trunk-line, it being understood that after the calling subscriber has caused a selector to pick out the desired group of second-selectors or connectors, as the case may be, the desired con- Specification of Letters Patent.

Patented May 30, 1916.

Serial No. 258,508.

nection is then established with the first trunk-line which is found idle, or with the first connector which is found idle; for the arrangement is such that the calling sub scriber may use any one of a certain number of second-selectors, or of connectors, as the case may be, for establishing a through connection to the line of the called subscriber. In other words, the subscriber may use any one of a certain number of trunkline connections for making connection between his line and the line of the called subscriber; but when the connector is operated, it is then essential, of course, that both the vertical and rotary movements of the switch-shaft thereof be under the direct control of the calling subscriber, so that the latter may not only cause the connector to pick out the particular group in which the called subscribers line is included, but may then also pick out the line running to the called subscribers station.

As stated, the automatic telephone s stem to which my invention more especial y relates is of that type in which the selectors and connectors are operated on the stepby-step principle-that is, by means of ratchet mechanism adapted to give the switching contacts a step-by-step progressive movement in response to separate and distinct electrical impulses transmitted from the station of the calling subscriber.

Generally stated, the object of my invention is the 1provision of an improved, sim plified and iighly etlicient telephone system of the foregoing general character.

A specia object is the provision of an improved construction and arrangement by which the current, both for talking and switching purposes, may be furnished from a common attery or other centralized source of supply located at the exchange or central station.

Another object is the provision of a construction andiarrangement whereby the current for talking purposes may be advantageously supplied to the talking circuit through certain switch-contacts of the connector employed in establishing the connection between the calling and called subscribers lines.

A further object is to provide such a construction and arrangement of circuits and parts as will permit the switches to be released or restored over release-circuits" ineluding certain so-called private-wipers and private-bank-eontacts of the said switches, and in a system in which the current for talking purposes is supplied, as stated, from a common battery through the connectors to the talking circuits established between different subscribers.

Another object is to provide means for establishing the llow of talking current in the calling line when the called subscriber answers.

t is also an object to provide certain details and features of improvement tending to simplify, improve and increase the efiiciency and serviceability of an automatic common battery telephone system of this particular character.

To the foregoing and other useful ends, my invention consists in matters hereinafter set forth and claimed.

In the accompanying drawings, Figure 1 is a diagrammatic representation of circuits and switching mechanism employed when a subscriber at sub-station designated as No. 321 calls the subscriber at sub-station No. 220. To the left of the line X-X is represented that part of the switching apparatus known as a first-selector, belonging to the calling subscriber. T0 the right of the line YY is represented the same part belonging to a called subscriber, and between lines XX and YY that part of the switching apparatus known as a connector. Fig. 2 is a diagrammatic representation of one of the unit parts of the switching apparatus known as a first-selector-switeh together with bank terminals 43 and 47 of trunking lines that lead to connectors. Fig. 3 is a diagrammatic perspective representation of one of the unit parts of the switching apparatus known as a connectorswitch, together with bank-terminals 169 and 173 of trunk-lines that are connected with the subscribers lines, which trunk-lines are known as normal-trunks; V and R representing a pair of so-called line-normals, and 242 a so-calledprivate-normal. Fig. 4 is a simplified diii ram showing the method of distributing tie talking-current from the common battery to the talkingcircuit, and of charging the transmitters at the sub-stations.

Each sub-station is provided with the usual transmitter, induction-coil, ringer receiver and switch-hook, together with a keyboard, push-button and other essential details of construction and arrangement for operating and controlling the switching apparatus or mechanism at the central station.

The first-selector may be of any suitable, known or approved construction as represented in Fi 2), and may comprise the usual vertica and rotary relays 18" and DI; the bridge cut-oll' relay ears; the rotary and vertical magnets 82 and 27",

together with the release-magnet 56, the private-magnet 59, and the back-releaserelay Other familiar features of a switch of this character are: a shaft having circular ratchet-teeth by means of which it is given a step-by-step longitudinal or endwise movement by the vertical-magnet 27"; said shaft also having longitudinal ratchet-teeth by means of which it is given a step-by-step rotary movement by the rotary-magnet 82 through the medium of any suitable, known or approved mechanical connections. On the said shaft are supported the so-ealled line-wipers or conductingarms 44" and 45", and the private-wiper or conducting-arm 42. This first-selectorswitch is also further identified, it will be seen, by the cireuit-changing-arms or wipers 73, 74", 21" and 51' mounted on a shaft 188 which is attached to the arm (59, the whole comprising a so-called side-switch which is operated in the usual well known manner by privateanagnet" 59", through the medium of any suitable or approved mechanism. The connector-switch operates on the step-by-step principle, like other switches, in a well known manner, and may be of any suitable, known or approved character; but in this case certain novel circuit arrangements and features of construction are provided, in addition to the elements or features usually found in a connectorswitch of this character. For example: the said connector may comprise the usual vertical and rotary relays 109, 141; the release-magnet 311; the ringing-relay 254; and the private-magnet 146. Other familiar elements in a switch of this character consist of vertical and rotary magnets 119, 171which are employed as in other s\vitches-for imparting longitudinal and rotary step-by-step movements to the shaft 138 on which are mounted the usual wipers 170, 171 and 168.

The connector is further identified by the usual side-switch provided witn switching-arms 128, 158, 159 and 160, said side-switch being operated by the private-niagnet 146. There are, however, certain novel elements or features ineludcd in the construction of said connector For example: the ditlcrential-rclay 187 by means of which a calling subscriber is enabled to restore his switching apparatus to its normal condition when a called sub-- scriber fails to restore his receiver to its hook, and by means of which it called subscriber is enabled also to break the connection established with his line if the calling subscriber neglects to do so; also the socalled magnet-cut-ofl-relay 280 used to control local internal circuits in the connector. and a polo-changing relay 281 by means of which the polarity of certain circuits are changed in order to provide the current nccerator D, and may or may not make use of the common battery which provides current for talking and other purposes. Underneath the switches at central station are mounted banks 43" and 47" (Fig. 2), and 169 and 173 (Fig. 3) of a well-known or any suitable character.

Assuming that the switching apparatus or mechanism is in its normal condition, as shown in Fi s. 2 and 3, and that subscriber at the le t (Fig. 1)which we have designated as No. 321wishes to establish connection with the subscriber at the substation at the right-designated 220, his first act will be to remove the receiver l from switch-hook 2. This operation closes springs 3 and 4, springs 5 and 6, and springs 7 and 8. He now presses the pushhutton 9 two times in succession, disengaging spring 10 from contact with spring 11 twice, and making contact with s ring 12 twice. This energizes the so-calle vertical-line-relay-coil 13' of selector S twice in succession through the following circuit: from the non-grounded pole of battery 14 over conductors 15, 352' and 16', s rings 17' and 18, conductor 19', relay-coil 13', contact-point 20, switching-arm 21', con ductor V, springs 10 and 12, conductors 22 and 300, springs 7 and 8, conductor 23 to ground G, to the grounded terminal G of battery 14. Referring to Fig. 2, the vertical-line-relay 13' has energized twice, actuates the armature 24" twice, and closes contact between springs 25' and 26' twice, thus energizing vertical-magnet 27' twice through the following circuit: non-grounded pole of battery 14, conductors 15, 57", 28" and 29", vertical-magnet 27', conductor 30, sprin s 31' and 32', springs 25 and 26" to grounfG and to grounded terminal G of battery 14. This actuates the vertical-armature 34' twice in succession, to which is fastened the arm 35 having the L- shaped piece 36" and pawl 37'. the latter being subject to the tension of the spring 354". The first movement of armature 34', which is pivoted at points 356' and 357", and which is always subject to the tension of the spring 353", disengages the so-called release-link 38" from lug 329 on the socalled double dog 39' by means of the L- shapcd piece 36'. Said double dog is now left free to respond to the tension of the retracting spr1ng 40", and its arms 354" and 355" are drawn against the circular and longitudinal teeth 91' and 92, respectively. At the same time that the release-link 38 is disengaged from the double dog 39*, the shaft 41" is raised one step by pawl 37". the latter engaging with the circular teeth 91. As the sha t is raised, the arm 354 of the double dog 39 engages with said circular teeth and retains the shaft in its raised position. The next impulse raises the shaft 41' another step in the same manner; the subscriber thus bringing the wiper 42 opposite the first contact of the second row of so-called private-lamk-terminals 43", and at the same time bringing wipers 44" and 45', which are separated by insulating material 46", opposite the first contact of the second horizontal row of trunk-lineterminals 47*.

Referring to Fig. l, the next act of the operator consists in pressing the button 48 once, thus causing the spring 50 to break connection with the contact 49, and to make contact only once with spring 12. This momentarily energizes the rotary-line-rclay 51' of selector S through the following circuit: non-grounded pole of battery 14, conductors 15 and 16, springs 17, 1S and 52, relay-winding 51',contactpoint 53", switch-arm 54", conductor R, spring 50, spring 12, conductor 22, springs 7 and 8 to ground G, to grounded terminal G of batteiiy 14.

eferring to Fig. 2, magnet 51', thus energized once, actuates the relay-armature 7' once, thereby bringing springs 55' and 26" into contact once, and in turn actuating the private-magnet 59' through the following circuit: non-grounded pole of battery 14, conductors 15, 57 and 58, private-magnet 59, conductors 60 and 61', springs 55' and 26' to ground G, to grounded pole G of battery 14. This actuates the privatemagnet-armature 62 once, to which is attached an arm 63 having a saw-tooth escapement consisting of teeth 64', 65', 66" and 67' and an arm 68', and which swings on pivots 35S and 35!)". As the private-armature G2 is attracted, the arm 69" which constitutes part of the socalled side-switeh-disengages from tooth 64' under the tension of spring I0". and falls against tooth 65", but from which it in turn disengages when the armature 62* returns to its normal position. Further movement of the arm (30' is checked by reason of lug 71" striking against a cam 72": and at this time the side-switch-wipcrs 73", 74", 21" and 54' have shifted from the first position. in contact with points 102", 103', 20" and 53*, to the second position and into contact with points 75", 76", 77 and T8. respectivelv: and the side-switch-wiper 73, having now closed with the contact-point 75", causes the coils 79" and 80" of the rotary-magnet to be energized through the following circuit: 1

non-grounded terminal of battery 14, conductors 15, 57' and 81, rotary-magnetcoil 7 9, springs 83 and 84", rotary-magnetcoil conductor side-switch-wiper 73, contact 75' to ground G, and to grounded terminal G of battery 14. The energized coils '79 and 80' actuate the rotary-armature 86'which is pivoted at points 360 and 361'-and on said armature 86' is found the so-called,rotary-armature finger 88', interrupter-arm 87', and the arm 89' on which is fastened the so-called rotary-pawl When the rotary-armature 86' is attracted by the magnet-coils 79' and 80', the said rotary-pawl engages with the longitudinal teeth 92 on the shaft 41', causing the latter to rotate one step. As the shaft is rotated, the arm 355 of the double do" 39 engages said longitudinal teeth, retaining the shaft in the advanced position. This brings private-wiper 42 into engagement with the first contact of the second row of so-callcd private-bankterminals 43', and the line-wipers 44' and 45' into engagement with the first contacts of the second row of line-banks 47. At the same time that pawl 90' begins to rotate the shaft 41' one step, as explained, the rotary-armature-finger 88' begins to press the private armature 62' toward the pole-piece of private-magnet 59'. As soon as the cam 72' has rotated away from lug 71, the side-switch-finger 69' falls against tooth 66 on the arm of the Private-armature. By the time the wipers 42, 44 and 5" are moved to the first contacts of the second level of the bank-terminals, as was stated, and arm 69" disengaged from the tooth 66", the interrupter-arm 87' is drawn in far enough to break the circuit that energizes electro-magnets 79 and 80, by separatin springs 84 and 83". This will allow the rotary-armature 86' to return to its normal position, under the influence of a netracting spring 93", which, at the same time, allows the prlvate-magnet-armature 62" to regain its normal position. This allows the side-switch-finger 69' to disengage with tooth 07", and to shift the side-switchwipers 73", 74', 21" and 54' out of second position and into contact with points 94', 96" and 97', respectively; and this last position is known as the third position oi the side-switch.

The side-switch-wipers 21" and 54' having moved into contact with the points 90" and 97", respectively, the subscribers lineconductors V and R are thereby extended through said wipers and said contacts to conductors 99' and 98' to line-wipers 44' and 45", and through the bank-conductors and over the selected trunk-line to some disengaged connector, as ,will hereinafter more fully appear. At the same time, the side-switch-wiper 74', having engaged with contact 95', a guarding potential is thereby established at the first contact of the second row or level of private-bank 43*, by putting it in connection with the grounded terminal G of battery 14, as follows: grounded terminal G of battery 14, ground Gr at side-switch, contact 95, wiper-arm 74', conductor 99, so-called back-releaserelay conductor 101', private-wiper 42' to first contact in second level of private-bank 42'.

Referring to that stage of the call before subscriber #321 had pressed button 18, it will be seen that the shaft 41" has been raised two steps, and that the shaft-wipers are each opposite the first contact or terminal of the second level of their respective banks. It may be assumed that the first nine trunks or trunk-lines of the second level are in use by first-selector-switches similar to the one shown in Fig. 2. The switch using the first trunk in the second row will have its private-wiper--which is similar to private-wiper 42'in engagement with the first contact of the second row of a privatebank similar to the private-bank 43 with which it is connected in multiple. Also, with this arrangement, the side-switch of said other selector is in the third position and its wiper-similar to the side-switch-wipei" 74"-is in contact with a third contact similar to contact 95', thus bringing it into con nection with the grounded terminal G of battery 14. The private-wiper of said other selector being connected with a grounded side-switch-wipei, as privatewiier 42, a guarding potential is establis ed at the first contact of the second row or level of all private-banks similar to private-bank 43 with which it is connected in multiple; and the same will be the case with the other eight busy trunks. Now, it subscriber No. 321, after having pressed button 9 twice in succession, then presses button 48 once, he will then energize, as before, the private-magnet 59. This will again cause the private-magnet to attract its armature 62", disengaging side-switchfinger 69' from teeth 64', and bringing it against tooth 65" from which it also disengages when said armature 62" resumes its normal osition. Again, as before, the sideswitch-inger 69" will be found between teeth 66" and 64' and prevented from further forward advance, under the influence of retracting spring 70' by reason of the lug 71" striking the cam 72".

The side-switch-wipers having shifted from first position to second position, and into electrical connection with contactpoints 75, 76', 77' and 78'; and side-switchwiper 73' moving into contact with point 75", as before, will cause the energizing of coils 70 and 80" of rotary-ma net. The rotary-armature" 86" will now be attracted once, rotating shaft 41' gaging private-wiper 42' with the first contact of the second row or level of bank 43, allowing side-switch-arm or finger 69' to fall against teeth 66. Owing to the gnardin potential established by the other sclector or occupying-switch-which we have supposed is using the trunk-line corresponding to the first contact or terminal of the second level-as soon as privatewiper 42" engages with said contact, and before the rotary-arnniture has started to return to normal position, the irivate-magnet" is energized through t to following circuit: from the grounded terminal (1: of battery l-l through occupying-switch and circuit not shown, to first contact of second row of private-bank 43'', to privatewiper 42", conductor 101", lmck-release-relay 100, conductor 9!)", side-switch-wipei 74', contact-point T6", conductors 98 and (30', private-magnet '9", conductors.58', 5T", 15 to non-grounded pole of battery 14. Thus energized. the prirate-magnet 59 attracts its armature (32" and relieves rotaryarmature-finger 88' of its guardin dutv over the said armature-side-switci-arm 69" disengaging with tooth (36' and falling upon tooth (37; and shortly after the retary-pawl 90' has rotated shaft 41' sntiiciently to permit the double dog 39' to engage with the first longitudinal or rotarytooth 92', the interrupter-arm 87' will then be drawn forward sutliciently to separate springs 84" and 83; thus breaking the circuit through rotary-magnet-coils 79" and and permitting the rot-ary-armature 86" to fall back to its normal position, owing to the tension of the spring 93'. It will be noticed, however. that the private-armatura W2" is still held down by the circuit established through the private-magnet as a result of the guarding potential encountered at the private-lmnk-contact. As soon as the rotary-arinature 86" has returned to its normal position. springs 84 and 83 again make contact with each other, thus again energizing coils T9 and 80 of the rotary-magnet" through the same circuit as before: and this will again actuate rotar v-arinature" S6" and then cause rotarypawl" to engage with the longitudinal teeth 92". and to rotate shaft 41' one step more. and to shift the private-wiper 42, together with the line-wipers 44 and 45, to the second contacts of the second level of their respective banks. As this second contact is also characterized. at this time, by a guarding potential, the private-armature 62" will remain in its attracted position by reason of the circuit already described. As soon as the longitudinal teeth 92" have been advanced far enough to allow the double dog 39' to engage with the second teeth, the interrupter-arm 87' on the toone notch, and entary-armature 86 again breaks the circuit through the rotary-magnet, and again falls back to its normal position. As soon as it does so, however, springs 83' and 84 again come into contact with each other, causing the rota ry-arinature" 86" to rotate the shaft 41' another step. This will be repeated as often as private-wipei" 42' continues to encounter pr1vate-contact-points in private-bank" 43' with an established guarding potential. When the shaft 41' has won rotated nine steps, the private-wiper 42' will then engage the ninth contact ot the second row or level, which also has a guarding potential. The rotary-lnagnet will he energized once more, and shaft 41' will be rotated one more step, moving privatewiper 42' onto the tenth contact-which latter has no guarding potential-as it is not busy. As soon as the privatewipei" 42" leaves the ninth contact, the circuit through the private-magnet 59' is broken and the private-arinature 62 is restored to the charge of the rotary-armaturefinger 88. As soon as the circuit through the rotary-magnet is again broken by arm 87". the rotary-armature" 86" then falls back again for the last time, allowing private-armature 62 to resume its normal position. The side-switch-arm 69 will then disengage from teeth 67' and fall against stop 189", shifting all the side-switch- 'ipers 73', 74, 21 and 54 to third position, and thus extending the calling subscrihers .line-conductors V and R-as before-to a connector not in use, through the linewipers 4 0 and 1&5". and over trunk-line-conductors 115 and 143, as clearly indicated in Fig. 1.

Referring to Fig. 2, again it will be observed that the side-switch-wiper 7t, being in the third position, is in contact with point thus establishing a guarding potential at the tenth contact of the second row or level of the private-bank 43 through a circuit already described. It will also be seen that while private-wipe1" 42 was passin over the contacts having a guarding potentlal, the private-magnet 59 was energized through relay-coil but this latter coil is of such low resistance as not to interfere with the working of coil 59; and at the same time coil 59 is of such comparatively high resistance that the current passing through coil 100', when they are both in series, is of such small strength that the magnetic force generated is not sutlicient to draw down its armature 322 against the tension of spring 320. The subscriber having thus extended his line to the proper connector (see Fig. 1), he will now press the button 9 twice in succession. This will again separate spring 10 from spring 11 twice, and also twice bring it into contact with the spring 12. This energizes the vertical-line relay coil 109 twice in succession through the following circuit: nongrounded terminal of battery 14, conductors 15, 110 and 111, springs 112 and 113, winding 114 of differential-coil 187, vertical-line-relay 109, conductor 115, wiper 44', conductor 99', contact-point 96', switching-arm 21', conductor V, spring 10, spring 12, conductor 22, spring 7, spriu 8, conductor 23 to ground G, and throug 1 ground to rounded terminal G of battery 14.

eferring to Fig. 3, the energizing twice of the vertical-relay-coil 109 causes relayarmature 116 to be twice attracted, thus twice closing contact between springs 117 and 118; and this twice energizes the vertical-magnet 119 throu h the following circuit: non-grounded poe of battery 14, conductor 15, conductor 120, springs 142 and 257, spring 258, conductor 123, conductor 124, conductor 125, vertical-magnet 119, conductor 126 contact-point 127, switching-arm 128, conductor 129, spring 265, spring 266, conductor 132, springs 117 and 118 to ground G, and to grounded terminal G of battery 14. Thus energized, the vertical-ma net 119 actuates the vertical-armature 133 twice-being pivoted at points 105 and 106and provided with the arm 134, the L-shaped piece 135, and the so-called vertical-pawl 136. The 'pawl 136, under the tension of the retractmg spring 362, engages the teeth 137 and raises the shaft 138 one step. At the same time, the L-shaped iece 135 disengages the double dog linl: 139 from the double dog 140, thereby allowing the latter to drop into engagement with teeth 137 to prevent the shaft from falling back to its original position while in operation. After the vertical-armature returns to its normal osition, under the tension of the retracting spring 363. a second impulse causes the iawl 136 to again engage with circular teet i 137, raisin the shaft 138 one more notch or step, an thus bringin the private-wiper 168 opposite the irst contact of the second row or level of private-bank 169, and line-wipers 170 and 171, which are insulated from each other by suitable material 172, opposite the first contact of the second row of line-bauk-terniinals 173. It will be noticed that when the subscriber at sub-station No. 321 (Fig. 1) enerized vertical-line-relay 109, by pressing button 9, the circuit was closed through winding 114 of differential coil 187.

The differential-relay has two windings and is constructed in such a manner that its armature 365 (Fig. 3) is only energized while currentis passing through one of the windings, or when the coils are in multiple, but not whenthey are at in series by the act of the'called subscri 'er in taking down his receiver; so that the armature 365 will be actuated in unison with the armature 116 of the vcrtical-line-relay, but its actuation at this time has no significance or utility. In the next step, the subscriber No. 321 (Fig. 1) presses the button 48 once, which disengages spring 50 from contact 49 once, and brings it into contact with spring 12 once; and this causes the rotary-linerelay 141 to be energized once through the following circuit: non-grounded terminal of battery H, conductors 15, 110, 111, spring 142, winding 143 of differentialrelay 187, rotary-relay 141, conductor 314, wiper 45", conductor 98", wiper 54", conductor R, spring 50, spring 12, conductor 22, springs 7 and 8. conductor 23, and ground G to grounded terminal of battery 14; and this in turn energizes the privateiuagnet 146, only once, through the following circuit: non-grounded terminal of battery 14, conductors 15, 110, 111, 256, spring 142 and 257, conductors 303 and 147, private-magnet 146, springs and 118 to ground G, to grounded teriuinal G of battery 14.

Referring to Fig. 3, thus energized the privatemagnet 146 actuates the privatearmature 150. On this armature. which is pivoted on points 363 and 364, are found the arm 151, a ratchet or saw-tooth escapement with teeth 152, 153, 154 and 155, together with arm 156. \Vhen the privatearmature 150 is attracted, theside-switcharm 157 disengages from the tooth 152 and comes in contact with the tooth 153, but from which latter it disengages when the private-armature 150 regains its normal position under the influence of the retracting-spring 108. The sideswitch-wipcrs 128, 158, 159 and 160 are, in this way, moved from their first position in contact with points 127, 161", 162 and 163, respectively, to what is known as the second position, and in contact with points 164". 165. 166 and 167, respectively.

The next operation of subscriber #321 (Fig. 1') consists in pressing button 9 ten times; and this disengages spring 10 from spring 11 exactly ten times. and brings it into contact with the spring 12 ten tunes. thus energizing the rertical-liue-relay" 109 ten times through the same circuit as before. In Fig. 3, the vertical-liue-rela 109, thus energized ten times. in turn actuates the relay-armature 116 ten times, thus bringing together springs 117 and 1133 ten times, and in'turn energizing rotary-magnet 174? ten times through the following circuit: ;n-grminded terminal of battery 14, condiu rs 15 and 120, springs 142, 257 and 258, 0 uctors 123, 124 and 175, rotary-magnet 574, conductor 176. contactpoint 164, .j, switch-wipcr 128, conductor 129, sp," s 265 and 266, conductOIS 132, and 1 I snrings 117 and 118,

conductor 149 to ground G and to grounded terminal G of battery 14. Thus actuated ten times, the so-called rotary-magnet 174 actuates the rotary-armatnre 178 ten times which is kept under the tension of retracting spring 181and on which are mounted the arm 179 and a soralled rotar \'-pa\\'l" 180, which latter is kept in its uoruml position by a retracting spring 182. As in the case of the tirst selector, each time that the rotary-armature" 178 is attracted. the rotary-pawl 180 engages the teeth 183. thereby rotating shaft 188 one step against the tension of spring 184, but the shaft being held at each step by the arm 185 of the double dog 140; for at this time. said arm engages the teeth 183. and is held in such engagement by the tension of the retracting sprin 180. .-\t the end of this operation. the line-wipers 170" and 171 will be. found on the tenth contact of the second row or level of line-bankterminals 173, this particular contact or terminal being connected with the called subscribers line, which latter is not busy; and private-wiper 108 will be found on the tenth contact of the second row or level of the privatc-bank-terminals" 109.

The next act of the subscriber No. 321 (Fig. 1) consists in a ain pressing the button 48 once, and thereiiy disengaging sprin 50 from the contact 40, and closing it wit\ the spring 12, and again actuating rotaryline-relay" 111 in the usual manner. Prirate-magnet 110, being thus energized but once, actuates the prirate-armature 150 but once, causing the side-switch-arm" 157 to disengage from tooth 154 on its downward stroke, and from tooth 155 on its return to normal position, and falling against stop 191, owing to the tension of retracting spring 190. Side-switch-wipcrs 128, 158, 159 and 100 will, at this time, be drawn to the third position and into contact with points 191, 195. 190 and 197, res )cct-irely. This final operation connects the ca ling subscriber with the subscriber called, through the socalled normal-trunk-line-conductors V and R". shown more clearly in Fig. 1, as follows: calling subscribers line-conductor" V, switching-arm 21", contact-point 90", comltletnl 99, wiper 14", conductors 115 and 198, condenser 199, conductors 200 and 201, springs 202 and 203, conductor 201, switching-arm 159. contact-point 190. conductor 207, wiper 170, conductor V", conductor V, spring 208, contact 209, conductors 210 and 211, book 212, spring 213, ringer 21 1, conductor 215, condenser 210, conductor 217, contact 218, spring 220. conductors R and R, wiper 171, switchingarm 100, conductor 222, springs 223 and 221, conductors 225 and 220, condenser 227, conductor 228, wiper 45', conductor 98', contact-point 97', wiper -1, line-conductor It, spring 50, contact 49, conductor 229. condenser 230, secondary winding 231 of induction-coil 230. conductor 282, receiver 1, conductors 233 and 231, springs 3 and -l, conductor 2215, contact 11, spring back to conductor V.

In Fig. 1, the shifting of the side-switchwiper 158 into contact with point 195 establishes a guarding potential at the prirate-contact with which private-wiper 108 is now in contact, as well as at all other private-contacts connected with it; and this by reason of the fact that. electrical connection has been established with the grounded terminal (1 of battery 11, through the following path: grounded terminal G of battery 11 to ground (1 at the sideswitch, contact 195, wiper 158, conductor 238 to private-wiper 108 to privatecontact which is in connection with the socalled normal-trunk-conductol" 212". At, the same time that a uarding potential is established at the tenti contact of the second row or level of the private-bank 109, a circuit is also established by way of said contact and along the private-normal" 242" (as is clearly shown in Fig. 1), which energizes the so-callcd cut-011' relay 239 of the called subscribers first-selectorswitch, through the following circuit: non-grounded terminal of battery 14, conductor 15. magnet 2219', contact 210", spring 241, conductor 2-12", wiper 108, conductor 238, switching-arm 158, contact-point 195 to ground (1 to grounded pole G of battery 14. Thus energized the cut-011' relay-magnet 239 attracts the armature 243", separating springs 214", 245" and 2-10", and thus cutting 00 the bridge formed bv the line-relays 2-17 and 218 across the lineconductors V and R, and which is ordinarily closed through the following circuit: liue-conductor V, switching-arm 219, vertical-1ilie-relay 217, springs 245" and 2-10", rotary-line-rclaW 2-18, switchingarm 250 to line R. The object of opening this bridge is two-fold, and will again be referred to in the following description. The subscriber at sub-station #321 is now ready to ring the bell at sub-station #220, and he. therefore presses the button 250, which causes spring 251 to break contact; with spring 252 and close contact with spring 253; aml this will cause the vertical-linc-relay 109 to again be energized as follows: non-grounded terminal of bat tery H, conductors 110 and 111, springs 112 and 118, winding 114 of ditl'erential-relay 187, vertical-linc-relay 109, conductor 115, wiper 4-1, conductor 99", contact 00", switching-arm21", line-conductor V, spring 10, contact 11, conductor 2215, springs 1 and 3, conductor 2211, springs 5 and 0, springs 251 and 253, springs 7 and 8 to grounded terminal G, and to ground G of battery 14. The differential-relay is energized with the vertical-relay, but is of no conseguence or utility at this time. Thus energize the vertical-line-relav will operate relay-armature which will close contact through springs 117 and 118, and thus in turn energize the so-called ringer-relay 254, through a circuit as follows: noirgroundcd terminal of battery 14, conductors 15, 110, 111, 250, springs 142, 257, 258, conductors 250 and 200, ringerrelay 254, conductor 201, contact-point 104, switching-arm 128,. conductor springs 205 and 200, springs 117 and 118 to iouud G and to grounded terminal G of iattery 14. Thus energized, the ringer relay attracts the armature 300, thereby separating spring 223 from 224, and bringing it into contact with spring 207, and at the same time separating sprin 203 from spring 202 and bringing it into contact with spring 208. Springs 203 and 223 constitute terminals of sub-station N0. 220, and springs 224 and 202 the terminals of sub-station No. 821, while springs 207 and 208 constitute the terminals of the ringing machine D; and it is evident that the action of the ringer-relay 254 separates the line of sub-station No. 220 from the line of substation No. 321, and closes it with the terminals of the generator D, as long as subscriber No. 821 is pressing button 250. In this way, the ringer or signaling apparatus 214, of subscriber No. 220, is energized through the followingDcircuit: brush 200 of ringer-generator conductor 270", springs 208 and 203, conductor 204, switching-arm contactoint 100, conductor 207, wiper con actors V" and V, spring 208, contact 200, conductors 210 and 211, hook-switch 212, spring 213, ringer 214, conductor 215, condenser 210, conductor 217, contact 218, spring 220, conductors 11 and R", wiper 171, conductor 221, switching-arm 100, conductor 222, springs 223 and 207, conductor 271', brush 272" and back to rin or machine D. The bells 214 of station ho. 220 will now ring until subscriber at sub-station No. 321 releases button 250. allowing relays 100 and 254 to again resume their normal condition. Springs 208 and 223 falling back upon springs 202 and 224, respectively, again establish connection between sub-station No. 321 and No. 220. Had not the cut-oilrelay 230 opened the bridge across the line conductors V and R. the rin 'n current would also have passed throng tie bridging vertical and rotary line-relays 247" and 248", energizing them and making it possible for the switch A to be operate since if the armatures 380" and 387" are attracted the springs 888 and 380 are grounded on the sprin 107", which would, as in switch 8, result in actuating the vertical and rotary magnets; and not only for this reason but also for the reason that it is desirable, as is well known, that during talking there be a minimum number of bridges across the talking line.

When the subscribei; at sub-station 220 answers by removing his receiver 273 rom the hook 212, the ringer-circuit will be opened at the junction of switch-hook 212 with spring 213, and the following sirings will close; 274 with 275, 270 with 27 and 278 with 270. Talking current will now be admitted on the line of sub-station #220, through its transmitter 284 and the primarywinding 282 of induction-coil 288, which current also energizes the magnet-cut-oiirelav 280 and the pole-changing-relay 281 of connector C, through the following circuit: non-grouiided terminal of battery 14, conductors 15 and 110, pole-changingrelay 281, conductor 225, springs 224 and 223, conductor 222, switching-aria 100, contact-point 107, conductor 221, wiper 171, conductors R" and R, spring 220, contact 218, conductor 217, primary-winding 282 of induction-coil 283, transmitter 284, contact-point 285, spring 280 to springs 270 and 277, conductor 287, springs 278 and 270, conductor 210. contact 200 to spring 208, conductors V and V, wiper 170, conductor 207, contact 100, switching-arm 150, conductor 204, springs 203 and 202, conductor 201, inagnet-cut-otT-relay 280, contact 288, armature 287, switching-arm 158, contact 105, ground G" to grounded terminal G of battery 14. The battery current for talking purposes is furnished from the common buttcry 14 to transmitter 284 and primary-coil 282 of induction-coil 283, through magnetcut-oiY-rclay 280 and iole-c hanging-relay 281, as previously stated, which, being energized, attract their respective armatures. Armature 280 of mamiet-cut-otY-relay 280, being attracted, causes contact between springs 258, 257 and 142 to be broken, thus disconnecting the operating magnets of the connector-switch C from battery 14, so that they will not be actuated when the armaturcs of the line-relays 100 and 141 are energized. At the same time that armature 280 is attracted by its magnet 280, arnuiture 200 is attracted by the polechiinging-relay 281, causing spring 118 to break away from spring 112, and to come into contact with spring 201. As soon as this occurs, talkin current is furnished to the line of substation #321 through the fol lowing circuit: non-grounded terminal of battery 14, conductors 15, 110, 111 and 250, winding 143 of difl'erential-relay 187, rotary-line-relaf 141, conductor 814, wiper 45", conductor 08", contact 07', switching arm 54", line-conductm R, spring 50, contact 40, conductor 220, priiuary-wiiuling 201 of induction-coil 230, transmitter 202, contact 252, spring 251 to springs 6 and 5, conductor 234, springs 3 and 4, conductor 235, contact 11, spring 10, line-conductor V, switchingarm 21", contact 96", conductor 99, wi er 44', conductor 115, vertical-line-relay 109, winding 114 of differential-relay 187, springs 113 and 291 to ground G, and to grounded pole of battery 14. When this circuit is established, battery current passes through both windings of iiferential-relay 187, which are so wound that in this case one coil neutralizes the other, leaving the armature 365 (Fig. 3) in its normal position. It will be seen that the current is furnished through line-relays 141 and 109, energizing them, and 116, respectively, being attracted; but as all the operating coils which are connected with springs 117 and 145, which are under the control of said armatures were disconnected from the non-grounded pole of the battery by the movement of the eut-off relay-iu'mature 289, the energizing of these line-relays has no effect upon existing conditions. Current alon the same path reaches transmitter 292 am primarywinding 291 of induction-coil 236, and the two subscribers are now ready to talk to each other.

When the subscriber at #220 speaks into transmitter 284, the resistance of'the circuit in which it is included with the primarywinding 282 of induction-coil 283 IS varied, causing the intensity of the current flowing to vary in unison. In this way, currents are induced in the secondary winding of induction-coil 293 at sub-station #220, in the usual way, which reach receiver 1 of subscribers station #321 through the following circuit: secondary winding 293 of induction-coil 283, conductor 294, receiver 273, conductor 295, conductor 287 to springs 278 and 279, conductor 210, contact 209 to spring 208, conductors V and V, wiper 170, conductor 207, contact-point 196, switching-arm 159, conductor 204, s rings 203 and 202 to conductors 201 an 200, condenser 199 conductors 198 and 115, wiper 44" conductor 99, contact 96', switching-arm 21", line-conductor V, sprin 10 to contact-point 11 to conductor 235, springs 4 and 3, conductor 234, conductor 233, reeciver 1, conductor 232, secondary winding 231 of induction-coil 236, condenser 230, contact-point 49, spring 50, line-conductor R, switching-arm 54", contact-point 97, conductor 98", wi er 45", condenser 227, conductors 226 am 225 to springs 224 and 223, conductor 222, switching-arm 160, contact-point 197, conductor 221, wiper 171, conductors R" and R, s ring 220, contact-point 218, conductor 21 to condenser 216, to secondary winding 293 of the induction-coil. It Wlll thus be seen that variations originating in the transmitter 284 of their armatures 144 sub-station #220 reach receiver 1 at substation #321 through an unimpeded path including the condensers 199 and 227. In like manner, variations produced in transmitter 292 at sub-station #321 reach the receiver 273 at sub-station #220. \Vhen one subscriber has established connection with another, the instruments may be released in different ways. The called subscriber may not have answered, in which case the calling subscriber releases by restoring his receiver; the called subscriber having answered, the calling subscriber may release by hanging up his receiver first; the called subscriber may attempt to make a call before the calling subscriber has released; and last of all, the called subscriber may hang up his receiver before the calling subscriber.

We will now suppose that sub-station #321 has called sub-station #220 withoutreceiving an answer, and that subscriber at station #321 hangs up his receiver on switch-hook 2; then finger 296 on switchhook 2 will engage with spring 297, pressng it onto spring 298, and 298 onto 299, bringing the three into contact at one and the same time. These springs are known as release-springs; and the result of pressing the said sprin s into contact is that the rotarv-line-relay is first ener ized from ground G through springs 8 an 7, conductor 300, conductor 301, springs 298 and 297, conductor 302, contact-point 49, spring 50 to line R, and, as before, through rotaryline-relay 141 to the non-grounded pole of battery 14, thus a ain actuating the armature 144 of this reliiy. By the attraction of armature 144, springs.118 and 145 will in turn be brought together, causing privatemagnet 146 to become energized through the same circuit already traced; the private-magnet thus energized in turn attracts its armature 150, causing springs 265 and 266 to break contact, thus breaking connection with ringer-relay 254, and closing contact between springs 306 and 307. Immediately after this takes effect, vertical-line-relay 109 becomes energized at the instant that the three release-springs 297, 298 and 299 come in contact with each other, as already explained, through the following circuit: ground G at sub station #321, conductor 23, springs 8 and 7, conductors 300 and 301, springs 298 and 299, conductor 308, contact 11, spring 10 to vertical-conductor V through vertical-line-relay 109, as before, to non-grounded terminal of battery 14. Thus energized, said coil attracts its armature 116, as before, bringing springs 309 and 310 into contact, and en ergizing the so-called release-ma net 311 of connector C, and the so-cal ed backrelease-relay 100' of selector S, through the following circuit: non-grounded termiml of battery 14, conductors 110, 111 and 250, springs 142 and 257, conductor 303, release-magnet 311, conductor 312, springs 309, 310, conductor 313, wiper 42, conductor 101', back release relay 100, switchin -arm 74, contact to ground G, to groun ed terminal G of battery 14.

The energizing of release-magnet 311 (Fig. 3) actuates the release-armature 315, which strikes the double dog 140, causing it to rotate about the pivots 340 and 341, and throwing lug 310 under slot 317, which latter is in the release-link 139. The link 139 then drops over In 310; and as double dog 140 is kicked in%) release armature 315, arm 334 on said ouble dog 140 in turn drives the link 335, which 18 on the side-switch-arm 157; the link 335 being driven in, as just explained, causes side-switch-arm 157 to rotate about the pivots 338 and 339, restoring side-switchwipers 128, 158, 159 and to their first positions, and causing side-switch-arm 157 to be restored to its normal position behind tooth 152. Shaft 138, thus left subject to the action of spring 184, rotates back on rest 192 until arm 318 strikes pin 319. At this juncture, rest 192 enters slot 320 again, and shaft 138, by its own weight, drops to its original position. At the same time that this occurs, back-rclease-relay 100 (Fig. 1), which is energized with release-magnet 311, attracts its armature 32'2", moving springs 320" and 321' into contact. In this way, release-magnet 50 of the selector S becomes energized through the following circuit: non-grounded terminal of battery 14, conductor 15, conductor 323", release-magnet 50', conductor 324", conductor 325, springs 320" and 321', ground G to grounded terminal G of battery 14.

Referring to Fig. 2, the release-magnet 50 attracts the releasearmature 320' against the pull of the retracting sprin 327. In this way link 38' is brought forwar and slot 228 falls over lug 329; and then when release-s rings 297, 298 and 299 (Fig. 1), at the suliscribers station, disengage from each other, retracting spring 327' draws the link 38' and double dog 39" back to their normal position. As the double do 39 is drawn away from the circular and ongitudinal teeth 91' and 92' by a rotary motion about the pivots 348' and 349, one of its arms 342' drives the link 343' along in the direction of its movement. Said link bein pivoted on arm 344" by a pin 845', and said arm 344" being a part of thefside-switca arm 09*, the result is that sideswitch-arm 09 is rotated about the ivots 340' and 347', causing it to be restore( to its normal position behind tooth 04", returning side-switchwipers 73", 74", 21' andlS-i" to their first positions; and shaft 41', being'left subject to fastened by a pivot 330 to the arm 337 the action of spring 330, rotates back upon rest 193 until arm 371 strikes the post 332. At this oint the rest 193 engages the slot 333, an shaft 41' drops of its own weight to its original position of rest, the whole switch being completely restored. Subscriber at sub-station #220 having answered, it may be supposed now that the subscriber #321 hangs up his receiver 1 on switch-hook 2 before subscriber #220 hangs up his receiver. It will be remembered that the magnet-cut-olf-relay 280 and the pole-changingrclay 281 are n an energized condition as well as verticaldine-relay 109 and rotary-line-relay 141. Now, as subscriber #321 hangs his receiver 1 on switch-hook 2, release-springs 297, 298 and 299 will be brought together, as before, with the result that vertical-line-relay 109 releases its armature owing to the fact that said coil is short-circuited through the ground, for the time being, as follows: ground G at sub-station #321, conductor 23, springs 8 and 7, conductors 300 and 301, springs 298 and 299, conductor 308, contact 11, spring 10, line-conductor V, switching-arm 21", contact-point 90, conductor 99, arm 44, conductor ,vertical-1ineaelay 109, winding 114of differential-coil 187, springs 113 and 291 to ground G.

Rotary-hne-relay 141 retain: its energized condition by circuit established as follows: non-grounded terminal of battery 14, conductors 110, 111 and 250, winding 143 of differential-coil 187, rotary-linerelay 141, conductor 314, wiper 45, conductor 98, contactpoint 97", switching-arm 54, line-conductor R, spring 50, contactpoint 49, conductor 30?, springs 297, 298, conductors 301, 300, springs 7 and 8, to grounded terminal G of battery 14. Under such conditions, it will be seen that current passes through only winding 143 of differential-coil 187, which separates spring 287 from contact 288. It will be remembered that this spring 287 forms part of the circuit for energizing magnet-cut-oflrelay 280 and pole-changing-rclay 281. As soon as this current is stopped, the armature 289 of magnet-cut-off-relay 280 resumes its normal position, with the result that the s rings 142, 257 and 258 are again broug it into contact with each other, rcstoring the operating arts of the connector C to their norma positions. As soon as this takes place, the private-magnet becomes energized throu h the usual following circuit: non-grounder terminal of battery 14, conductors 110, 111 and 250, springs 142 and 257, conductors 303 and 147, private-magnet 140, springs and 118 to ground G". Thus actuated, the private-magnet 140 attracts its armature 150, separating springs 205 and 200, and disconnecting ringer-relay as before, so that ringing current will not be uselessly projected to the called station. As soon as the differential-relay, by becoming energized, separates spring 287 from contact 288, the armature 290 of the pole-changing-relay 281 is restored to its normal position, causing spring 113 to break away from spring 291 and make contact with spring 112. At theinstant that this occurs, vertical-linerelay 109 becomes energized, as before, because the three release-springs 297, 298 and 299 are still together. Thus armature 110 of vertical-linc-relay 109, and armature 144 of rotary-line-relay 141, being attracted, at once bring springs 310 and 309 intocontact, there 1y causing the release-magnet 811 of connector G and back-release-relay 100' of selector S to become energized, with the result, as before, that all the switches are brought to their normal positions, the back-release-relay energizing the release-magnet of selector S.

Again, it may be supposed that the subscriber at substation #220 (Fig. 1) desires to make a call before subscriber at substation #321 has restored his receiver, and that the number he wishes to call is 9. He will, therefore, begin by pressing button 350 nine times; and the only resu t will be that every time spring 208 and contact 209 separate, ma'gnet-cut-oif-relay 280 and polechanging-relay 281 will be momentarily deenergized, theirrespective armatures falling back each time to their normal positions. The contact between springs 208 and 351 produces no result, for the onl thing accomplished'is the short-circuitmg of coil 280 through ground as follows: ground (3: at substation #220, springs 274, 275, conductors 352 and 353, springs 351 and 208,

conductors V and V", wiper 170, contactpoint 190, switching-arm 159, conductor 204, springs 203 and 202 conductor 201, magnct-cut-ofi-relay 280, contact 288, spring 287, switching-arm 158 and to ground G; but as soon as the button 382 is pressed, and contact between spring 220 and contact-point 218 is broken, the magnet-cutoff-relay and the pole-changing-relay will a ain fall back to their normal positions.

ow, as soon as 5 Wings 220 and 351 enga e on ch other, the poie-changing-relay 281 Wlll be momentarily energized through the following circuit: from ground G", springs 274 and 275, conductors 352 and 353 to spring 351, line-conductor It to the path already traced to the non-grounded ole of the battery 14, and again to groun at G. Thus energized, relay 281 will attract the armature 290, shifting spring 113 from spring 112 to spring 291. A circuit will now be closed, as before, through winding 114 of differential-relay 187 through vertical-line-relay 109 to substation #321,

back to rotary-line-relay 141, through the other winding of differential-relay 137 to the common battery. The line-relays 109 and 141, being thus energized, will again bring springs 310 and 309"- into contact, thereb energizing the release-magnet 311 0 connector C, and the back-releaserelay 100 of selector S, which in turn energizes the release-magnet 50 of the selector S, restorim the switches to their normal positions, as before.

If we now take a case where the called subscriber #220 hangs up his receiver first, the release-springs 397, 398 and 399 will be brought together by switch-hook 212, as at sub-station #321, with the result that both line-conductors V and R will be momentarily grounded as follows: from ground G to springs 274 and 275, conductor 352 to ground-spring 398, to springs 399 and 397, to springs 208 and 220 and to conductors V and R respectively. The grounding of conductor V will result in the short-circuiting of magnet-cut-ofY-relay 280 through ground in the manner already explained, which, bein tie-magnetized, restores the internal circuits of connector C. The pole-changingrelay 281 retainin its energized state, the switches will be refiaased just as in the case previous to this, where the subscriber attempted to call before the calling subscriber had restored his receiver.

Returning to that stage in the calling of #220 where the subscriber at sub-station #321 pressed the button 9 twice, and the button 48 once, the button 9 twice again, and the button 48 once, and for the last time the button 9 ten times-it only remains for button 48 to be pressed once to complete the desired connection. The position of the switches, it will be remembered, was as'follows: The first-selector S had cut-in or established connection with connector C, and connector C had been raised two steps, and had also moved around ten points or steps, the side-switch being in second position. Suppose, now, that subscriber #220 is busy; there are two conditions under which this may occur: First when subscriber #220 has been called by some subscriber, and, second, when subscriber #220 is callmg. Assume,'lirst, that the subscriber #220 has been called. Referring to Fig. 3, if this is the case, there is a connector-switch set on or connected with the line that leads to subscribers station #220, the wipers of which are set on the tenth contact of the second row or level of the respective banks, and the side-switch of which is in the third position. Guarding potential will, therefore, be found at the tenth contact of the second row or level of the privatebank 169, throu h a circuit similar to the following: roum ed terminal G of battery 14 to groum G of side-switch 158, condnctors 237 and 238 to private-W1 er 168, to busy-bank-contact. Now, i the subscriber at sub-station #321 pushes the button 48, (Fig. 1) the rotary line relay 141 will be energized in the manner already described, which will in turn cause the private-relay 116 to be energized through the circuit already described. The armature 150 of the pri\-'ate-relay 146 (Fig. 3) will be attracted as before, and arm 150 will separate springs 265 and 206 and close springs 300 and 307. In this way, the release-magnet 311 willbeenergized through the following circuit: non-grounded terminal of battery 14, conductors 15 and 120, springs 112 and 257, conductor 147, conductor 333, release-magnet 311, conductors 381 and 385, springs 307 and 300, conductor 308, contact-point 165, side-switch-arm 153, conductors 237 and 238, private-wiper 108 to tenth contact of the second row or level of the privatebanlc 100, which contact has a guarding potential supplied through some occupying-switch to ground (not shown) and to grounded terminal G of battery 14.

As soon as the release-magnet 311 is energized, the release-armature" 315 will e operated as usual, and the connector C will be restored to its normal 'position. The subscriber at sub-station #321 (Fig. 1), thinking that he has established connection, will press the signal-button 250, with the result that the verticaLune-relay 109 is energized as before; but instead of the ringer-relay 251 being operated, the vertical-magnet 110 is energized, owing to the fact that the side-switch is now in its first position, and the side-switch-wiper 128 in contact with contact-point 127. This circuit has already been pointed out and explained. As soon, therefore, as the vertical-magnet 119 is actuated, the shaft 138 (Fig. 2) is raised from its normal position, and the arm 318 on said shaft. being raised with it, will allow springs 370 and 309 to come into contact with each other. In this way, the receiver at sub-station #321 (Fig. 1) is brought into a circuit where current of any suitable nature is provided, this current usually causing a buzzing sound that will notify the subscriber that the party called is busy. This busy current may be prmluced in any suitable way. In Fig. 1 it is supplied by having a circuit-interrupter B inserted in the primary-circuit of a stepdown induction-coil 371". The primarycircuit of this induction-coil is as follows: non-grounded terminal of battery 14, conductors 15 and 374. primary-winding 372 of induction-coil 371. interrupter B to ground G to grounded terminal G of battery 14. This interrupted current induces a similar current in the secondary winding 373 of induction-coil 371", which reaches receiver 1 at sub-station #321 by the following circuit: secondary winding 373 of induetion-coil 371, conductor 308, contact 309, spring 370, conductor 380, switchingarm 1130", conductor 222, springs 223 and 221, conductors 225 and 226, condenser 227, conductor 228, wiper 45, conductor 93, contact-point 97, switching-arm 51, "liue-coiuluctor R, spring 50, contact-point 49, conductor 220, condenser 230, secondary windilu 231 of induction-coil 230, conductor 232, receiver 1, conductor 233, springs 3 and 4 conductor 235, contact-point 11, spring 10, 1ine-comluctoi V, switching-arm 21, contact-point 90", conductor 91)", wiper 11', conductor 115, \ertical-line-relay 100, windiug 114 of difl'erential-relay 187, springs 113 and 112, conductors 111 and 110, 15 and 371, and back to the second winding 373" of the induction-coil 371". The subscriber at sub-station #321 hea ring the busy signal, will know that the number he has tried to call is busy, and will hang up his reccivercalling some other time.

\Vhen receiver 1 is restored to its hook 2, release-springs 297, 208 and 299 will be brou ht into momentary contact, in the usua way; vertical and rotary linerelays" 100 and 141 will therefore become energized through circuits already traced, actuating the release-magnet 311 of the connector 0. and also the back-releaserelay 100 of the selector S, which will in turn actuate the release-magnet 56 of the selector S, restoring all of the switches to their normal positions in the manner already described. Suppose, however, that subscriber #220 is busy calling some other subscriber. It will be remembered that when the subscriber at sub-station #321 (Fig. 1) established connection with the subscriber #220, the private-wiper 108 of connector C established connection, also, over private-normal-line 2-12 with the cut-oll-relay 239 through springs 2-10 and 241. In this way, every first-selector is connected directly by way of a privatenormal-linc, similar to 242, with a prirate-contact in the connector-bunks, cor responding to its number. It is plain, therefore, that if subscriber #220 (Fig. 1) has made a call, the arm 37%), similar to arm 371, on shaft 11" will disengage with spring 211", similar to spring 370' (Fig. 2), allowing spring 241" to come into contact with spring 330. similar to spring 378. The result is that a guarding potential is established at the private-contact correspondiugtothe #220in the conncctorbanks, by connecting private-normal 242 to ground G" through springs 241" and 380. WVhen the subscriber #321 now tries to establish final connection, by pressing the button 48, the rotary-line-relay of connector C is actuated in the usual way, and in turn actnates the private-relay of said connector, in the manner already shown.

As soon as the private-armature 150 is attracted, springs 306 and 307 come into contact, and the connector-switch will be released as before, and the calling subscriber (Fig. 1), as soon as he presses the signaling button 250, will receive a busy signal in the manner already explained. He will then restore his receiver, again releasing all the switches and leavin them in readinessfor further calling. t may be that some time a subscriber will begin to make a call, and, not completing it, restore his receiver before the first-selectorswitch has cut-in or made a connection. For example: In Fig. 1, should the subscriber at sub-station #321 begin to make a call by pressing button 9 twice, the vertical-line-relay 13 of selector S will be twice momentarily energized, in the manner previously explained, raisin the shaft 41 (Fig. 2) to the second leve. Now, as receiver 1 is replaced on the hook 2, the release-springs 297, 298 and 299 will be momentarily brought into contact; the vertical-line-relay 13 will be momentarily energized through the following circuit: non-grounded terminal of battery 14, conductors 15, 352 and 10, springs 17' and 18, conductor 19, vertical-linc-relay 13", contact-point 20", switching-arm 21, verticalline-conductor" V, spring 10, contact-point 11, conductor 308, springs 299 and 298, conductors 301 and 300, springs 7 and 8, condnctor 23 to ground G to grounded terminal G of battery 14; and the rotary-linerelay 51 will be momentarily energized through the following circuit: non-groundrd terminal of battery 11, conductors 15, 352 and 10", springs 17' and 18' and 52', rotary-line-relay 51', contact-point 53', switching-arm 54', rotary-line-conductor ll. spring 50, cont-act point 49, conductor 130-3, springs 297 and 298, conductors 301 and 300, springs 7 and 8, conductor 23, ground (1 to grounded terminal G of battery 14. In this way, the armatures of the rotary and vertical line-relays 13' and 51' will be simultaneously attracted, armature 7' bringing springs 55" and 26' into contact and thereby energizing private-magnet) 59" through the following circuit: nongroundcd terminal of battery 14, conductor 15, private-magnet 59, springs 55' and 2G" to ground G, and to the grounded terminal of the battery 14.. Private-magnet 59', being thus energized, attracts the armature (32", causing spring 32' to break contact with spring 31' and close contact with spring 381"; at the same time, armature 21' of vertical-line-rclaybrings 25' and 26' into contact, energizing the release-magnet 56' through the following circuit: non-grounded terminal of battery 14, conductors 15 and 323", release-magnet 56', conductor 324, springs 381" and 32, conductor 387", springs 25 and 26 to ground G to grounded terminal G of battery 14. Thus ener ized, the release-magnet 56 (Fig. 2) will restore the switch to its normal position, in the manner already described, leaving it in readiness for further calling.

From the foregoing, it will be seen that I provide an exceedingly simple and highly cihcient common battery system in which the current for talking purposes is fed to the talking-circuit through the coils 109, 141, 114 and 143, at one side of the condensers 199 and 227, and through the coils 280 and 281 at the other side of said eondensers. In this way, only relay-coils are utilized for feeding the talking-current to the talking-circuit completed between subscribers stationsthat is, each and every coil through which the battery current is fed to the line-circuit for talking purposes is )rovided with an armature, and with suitable relay-contacts, and is thus characterized by functions other than that of acting as a resistance for regulating or limiting the flow of battery current to the talkingcircuit. Again, it will be seen that the battery current for talking purposes is fed to the linecircuit through the line-relays of the connectorthat is, at one side of the said condensers-and through the other relays 280 and 281 to the circuit at the other side of said condensers. \Vith this arrangement, the two line-relays 109 and 141, and also the relays 280 and 281, remain ener ized during conversation between the two su scribers; but at this time the differentially-wound relay 187 is not energized, owing to the fact that its two windings are connected in series with the battery 14 and the transmitter 292 at the calling subscribers station. Inasmuch as the connection between the non-grounded pole of the battery and the coil or winding 114 includes the normally open switch-springs 291 and 113 of the pole-changing-relay 281, it is evident that the calling subscribers-transmitter receives no talking-current from the battery until said pole-changing-relay 281 is energized, and the springs 291 and 113 thereby brought together, by the act of the called subscriber in removing his receiver from its switch-hook, in the manner already explained. The connection between the grounded pole of the battery and the magnet-cut-off-relay 280 includes the privateside-switch-wiper 158, and also the switchsprings 288 and 287 of the differentiallywound relay 187.

It will be seen that the various coilsin this case all relay-coilsthrough which the battery current is fed to the talkingcircuit, serve also as impedance for preventing the voice-currents from leaving the talking-circuit between any two subscribers stations and passing through the battery. In other words, the said battery is in bridge across the talking-circuit formed between any two subscribers stations, and the relaycoils are included in this bridge, and are also adapted to serve as impedance for preventing the shunting of voice-currents through the battery.

It will be readily understood that the different coils employed in the system can be of any suitable or desired resistance, according to the conditions of any particular case; but with respect to the connector I find that good results can be obtained by making the coils 100, 141, 280 and 281 of 500 ohms resistance each, and by making the coils 114 and 143 of ohms resistance each. The voltage of the battery can be regulated, according to requirements, and in accordance with the character of the exchange and the transmitters employed at the subscribers stations. In any event, however, the said relay-coils preferably have three functions, to-wit: the energizing of their cores for the purpose of opening and closing circuits; the retardation of any voice-currents tending to stray from the talking-circuits; and the admission to the talking-circuits of the requisite amount of current required for charging the transmitters at the subscribers stations.

The relay 187 may be energized at various times during the operation of connecting up one subscriber with another; but it is only usefully energized at one timethat is, when the calling subscriber hangs up his receiver and thereby releases the connectorswitch, and consequently the selector or selectors, employed, in the manner explained.

The magnet-cut-off-rclay 280 is only energized for one useful urpose, and this is when the called subscriber takes down his receiver and thereby completes a metallic circuit running to both sub-stations-one from the battery to the calling snbscribers station, and one from the battery to the called subscribers station; and at this time the two line-relays 109 and 141 being energized, and the springs 309 and 310 being closed together, and the ener izing circuit of the release-magnet 311 being thus closed at the springs of the line-relays, it becomes necessary to open a switch-point in the release-circuit in order to prevent the connector from releasing. Consequently, the magnet-cut-oif-relay 280 opens a switchpoint in the circuit of the release-magnet 311 as soon as it is energized, and also opens a switch-point in the energizing circuit of the private-magnet 146, which latter would be energized by the closing together of the springs 118 and 145 were it not for some provision to the contrary. In this way, the calling subscriber releases by simply energizing the difi'erential-relay 187, in the manner explained, and thereby (lei nergizingthe magnet-cut-otf-relay 280. When this relay is deinergizcd, it closes the switch-points in the circuits of the release-magnet and privute-magnet", which are open during conversation between the two subscribers. The releaseanagnet 311 being, at such time, connected in series with the back-release-relay of the selector, the closure of its circuit in this way effects a release not only of the connector, but also of the selector; and it is obvious that this method of release, over a releasecircuit including the private-bank-contacts, may be applied to any number of selectors-that is, any number which may be found necessary in establishing connection between the calling subscribers line and a connector.

The so-called pole-changing-relay "281 is adapted to be energized for two useful purposes, namely.the shifting of the verticalline-relay 109 from the non-grounded pole to the grounded pole of the battery, and the releasing of the connector by the called subscriber; For example: If the calling subscriber does not release, the called subscriber can then release, in the manner explained, by opening his circuit and immediately thereafter closing a grounded circuit through the relay 281, so as to energize the two line-relays: and the relay 280 being necessarily dei nergized at this time. it follows that the release-magnet" and the prirate-magnet" are energized in the manner previously described. In this way, either subscriber can release the switches. The called subscriber may release by simply hanging up his receiver; but regardless of this, and as previously explained, the called subscriber is sure to release the connector and other switches if he attempts to make a call before the calling subscriber has hung up his receiver.

The relay 280 may be called a magnetcut-ofi-relay, inasmuch as it is used for severing the connection between the magnets of the switch and the non-grounded pole of the battery, it being observed that the circuits for the vertical and rotary magnets, and also the release and private magnets, of the connector extend in parallel from the non-grounded pole of the battery through their respective coils and thence over different pathswhich are normally open-to the grounded pole of the battery.

The relay 281 may be termed a polechangmg-relay, inasmuch as it is used for seyermg the connection by which the two line-relays 100 and. 141 are norinallv bridged across the trunk-line and in addition for shifting the verticaldine-relay 109 from one pole of the battery to the other, in the manner explained. \Vhen the calling subscriber releases the connector the act of replacing his receiver on the switch-hook short-circuits the vertical-linerelay 109 and the dill'erential-winding 11-1", thereby opening up the called subscribers metallic line-circuit, and deenergizing all of the coils included in such metallic linecircuit. This, of course, results in the shifting of the \ertical-line-relay 109 from the grounded to the non-grounded pole of the battery, and in the consequent and immediate inclusion of these two line-relays in a grounded circuit in parallel with each other, thus closing the circuits through the release-ina miet and the private-magnet, in the manner explained. When the called subscriber releases, it will be seen that he does so through the medium of only the nonditl'erentially-wound electro-magnctic means in the connector, the ditl'erentially-wound moans remaining dei ncrgized. As distinguished from this, however, the calling subscriber can effect a release or restoration of the connector by and through the medium of the difi'erentially-wound-rclaythat is, when the calling subscriber releases, he does so through the medium of the differentiallywound relay. Obviously, the energizing of the private-magnet of the connector, when the calling subscriber releases, prevents a ringing of the called subscribers hell.

I obtain increased etliciency and simplicity of construction by using both of the linerelays of the connector for supplying talking-current to the talking-circuit established between subscribers stations.

The selector herein shown and described may be of the general type Shown and described in Patent No. 815,321, granted March 13, 1906, to Keith. Erickson & Erickson.

The connector herein shown and decribed may be of the general type shown and described in Patent No. 815,176, granted March 123, 1906, to Keith, Erickson & Erickson.

\Vith a view to insuring a positive or guarding potential at the private-bank-contacts of the selector, in case a third subscriber should attempt to cut-in on the circuit just at the time one of the subscribers is releasing the switches, the release-magnet of the connector may be of 0 ohms resistance and the releaserelay of the selector of one-half ohm resistance. In this way, it is possible to release over a circuit including the private-wipe! and privatebank-contacts of the selector without neutralizing the guarding potential established at the private-bank-contact -that is, the contact which is in use-by reason of the connection existing at that time between such contact and the grounded pole of the battery. In other words, the resistance between the non-grounded pole of the battery and the private-hailk-contact of the selector" is preferably much greater than the resistance between the grounded pole of the battery and said contact. Consequently, should another subscriber attempt to establish connection with the contacts of a selector corresponding to those already in use between two subscribers linesthat is, should another subscriber start the operation of another selector, the latter will not only refuse to make connection with the contacts corresponding to the trunk-line already in use for conversational purposes, but will even refuse to make connection with such contacts after the subscribers have finished talking and during the time that the release-circuit is closed; for by using the coil of the release-magnet of the conncctor a a resistance, in the manner specified, the necessary How of current will take place from the grounded pole of the battery, through the private-wipeN of the selector. through the priratelmnk-contact thereof. and thence through the privatewiper and bank-contact of the other selector, and with the result that the latter selector will continue its rotary motion even though the release-circuit between the selector and connector in use has been closed. This feature is, it will be seen, employed in a telephone exchange system in which the current both for talking aml switching purposes is supplied from the same common battery or centralized source of supply which energizes the release-magnet and release-relay and establishes a guarding potential at all private-lmnk-contacts which are busy or already in use.

It will be seen that no talking current is on the calling line, before the called subscriber answers. The callcd subscriber. in answering automatically establishes the. flow of such current in the calling line.

\Vhat I claim as my invention is:

1. An automatic common battery telephone systcm comprising a connector having switch contacts and line relay coils for controlling the operation of the switch, a common battery talking-circuit established through the switch-contacts of the connector and receiving current for talking purposes supplied from the common battery through the linc-relay-coils of said connector. and means for trunking a calling subscriber to the connector.

2. An automatic common battery telephcne system comprising a. connector having contacts and vertical and rotary linerelays, and talking-circuit established through the contacts of the connector and receiving current for talking purposes from the common battery through the windin s of the so-called vertical and rotarv line-relays of said connector.

3. An automatic common battery telephone system comprising subscribers lines, automatic switches including connectors, each connector being provided with the so-called vertical" and rotary line-relays, bridged across the talking circuit, and with connections whereb current for talking purposes is supplied rom the common battery through the coils of said relays to a calling subscriber's line.

4. An automatic common battery telephone system comprising subscribers lines, automatic switches and trunk-lines for connecting one subscribcrs line with another, each trunk-line having a pair of line relay coils normally bridged between its sides, said switches having step-by-step devices controlled by each of said relays, and connections whereby the current for talking purposes is supplied from the common battery through the said relays to the line-circuits.

5. An automatic common battery telephone system comprising subscribers transmitters, subscribers lines connecting the transmitters with automatic switching apparatus, said switching apparatus including connector-s" each provided with a pair of normally-brid '0(l line-relays, step-by-step devices contro led by each of said relays, together with connections whereby current for talking purposes is furnished from the common battery through the said relays to a subseribers line and transmitter.

(3. An automatic common battery telephone system comprising a connector provided with a. pair of normally-bridged lilierelays, a dill'erentially-wound relay having its windings connected in series in bridge between said line-relays, means for opening said bridge at a point between said windings when the connector is in use, and for including the common battery in the bridge at a point between the said windings, for the purpose of furnishing talking-current to the line-circuits.

7. An automatic common battery telephone system comprising a connector provided with a pair of normally-bridged linerelays, the middle point of the bridge between the two relays being normally connected with the non-grounded pole of the common batcry, means for shifting one of said relays from the non-grounded to the grounded pole of the battery when the called subscriber answers, means whereby the talking-current is supplied from the common battery through the coils of said relays to the calling subscribers line.

8. An automatic common battery telephone system comprising a connector provided with a pair of line-relays, a relay provided with suitable switch-contacts and adapted when dei nergized to connect the two line-relays in parallel with one pole of the common battery, but adapted when energized to shift one of said line'relays into connection with the other pole of said battery, together with means under the control of a callin subscriber for operating said line-relays," and means under the control of a called subscriber for ope 'ating said third relay.

9. An automatic common battery telephone system comprising two subscribers lines suitably connected together for conversational purposes, the means for connecting the two lines including a condenser in each side of the circuit, and also the switchcontacts of a connector, said connector being provided with electro-magneticallyactuated step-by-step devices, and with a pair of line'relays for controlling the operation of said step-by-step devices, the common battery being bridged across the talking-circuit at points each side of the said condensers, and the said line-relays constituting a medium of connection between the battery and that part of the talking-circuit included between the said condensers and the calling subscribefs station, whereby current for talking purposes is supplied from the common battery to the subscribers lines.

10. An automatic common battery telephone system comprising a "C()I1ll(5t0l" provided with suitable electro-magncticallypropelled switchim means, and with a pair of line-relays tl( apted to be operated by a calling subscriber for controlling the operation of said switching means, together with a magnet-cut-oll-relay and a polecbanging-relay adapted to be operated by a called subscriber for rendering the said switching means inoperative and shifting one of said line-relays from one pole of the battery to the other, and a differentiallywound relay adapted to be controlled by a calling subscriber and provided with means for controlling the operation of the said magnet-cut-ottrelay, the coils of all of said relays constituting a medium of connection for supplying current from the common liattcry to a completed line-circuit for talking purposes.

11. An automatic common battery telephone system comprising a connector provided with clectro-magnetically-operated switching means, and with a pair of linerelays for controlling said switching means, together with a magnet-cut-olf-relay and a pole changing relay, the magnet cut olfrelay being adapted when energized to render the said switching means inoperative, and the said polc-changing-relay being adapted when energized to shift one of said line-relays out of connection with one pole of the battery and into connection with the other pole of the battery.

12. An automatic common battery telephone system comprising a connector provided with a pair of normally-bridged line- 

